Fix response tracing for streaming response bodies

[jdisanti]

Tracing the response for a streaming body was omitting the actual body from the trace log:

TRACE smithy_http::middleware: response=Response { status: 200, version: HTTP/1.1, headers: ...}, body: SdkBody { inner: Streaming(Body(Streaming)), retryable: false } }

This change results in the actual response body ending up in the trace:

TRACE smithy_http::middleware: response=Response { status: 200, version: HTTP/1.1, headers: ...}, body: b"<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<LocationConstraint xmlns=\"http://s3.amazonaws.com/doc/2006-03-01/\">us-west-2</LocationConstraint>" }

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[rcoh]

We actually want something a bit more complex where if the response is handed off directly for streaming, we log it as a streaming body but if it gets read fully, we log the loaded body